Memory Mapping of 8085

Memory interfacing is used to provide more memory space to accommodate complex programs for more complicated systems. Types of memories which are most commonly used to interface with 8085 are RAM, ROM, and EEPROM.
8085 can access 64kB of external memory. It can be explained as- total number of address lines in 8085 are 16, therefore it can access 2^16 = 65535 locations i.e. 64kB.

Q. Design a minimum system to interface the following specification:
1. 32kB of RAM using 2 x 16kB RAM IC
2. 32kB of ROM using 2 x 16kB ROM IC

Therefore the spacing for all the 4 ICs are same due to same size of memory ie. 3FFFH.

The number of address lines required by each IC's is 14.

A15

A14

A13

A12

A11

A10

A9

A8

A7

A6

A5

A4

A3

A2

A1

A0

spacing

IC details

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0000H

ROM IC -1

0

0

1

1

1

1

1

1

1

1

1

1

1

1

1

1

3FFFH

0

1

0

0

0

0

0

0

0

0

0

0

0

0

0

0

4000H

ROM IC- 2

0

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

7FFFH

1

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

8000H

RAM IC- 3

1

0

1

1

1

1

1

1

1

1

1

1

1

1

1

1

BFFFH

1

1

0

0

0

0

0

0

0

0

0

0

0

0

0

0

C000H

RAM IC- 4

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

FFFFH

Interfacing Memories with 8085

Memories can be interfaced in two ways:1. Partial decoding: In this type of decoding not all the address lines are utilized in the circuit (they are left as unused pins). Ex: In an interface of 4kB memory only A0-A11 address lines are utilized, whereas the remaining A12-A15 address lines are unused.

2. Complete decoding (exhaustive decoding): In this type of decoding, all the address lines are utilized in circuit for some or the other use (i.e. all pins are exhausted). Ex: In an interface of 4kB memory only A0-A11 address lines are utilized, whereas the remaining A12-A15 address lines are used in Memory selection logic or as any other control signals.

About Us!

'Z Series Innovations' is an e-learning solution for learning all technical stuff online. It is an online portal that gives an enhanced way of learning and guidance in various fields of engineering which include robotics, electronics, communication,computer science, embedded systems and its real life applications.

Join Us

Do you feel like contributing to this website technically? Jump in!

Your technical expertise would be needed to create quality articles and content on this site and hence contribute to this growing global community of technical enthusiast.